1. Field of Invention
The invention relates to a light emitting diode, and more specifically to an AlGaInP light emitting diode
2. Description of Prior Art
The conventional AlGaInP light emitting diode (LED) with a double heterostructure, as shown in FIG. 6, includes a n-type GaAs substrate 3, a lower n-type (AlxGa1xe2x88x92x)0.5In0.5P cladding layer 4 with x=0.7xcx9c1.0, a (AlxGa1xe2x88x92x)0.5In0.5P active layer 5, an upper n-type (AlxGa1xe2x88x92x)0.5In0.5P cladding layer 6 with x=0.7xcx9c1.0, and a p-type current spreading layer 7 with high energy band gap. The material of the p-type current spreading layer 7 is selected from GaP, GaAsP, GaInP and AlGaAs.
The light emitting wavelength of LED varies with the Al composition of the active layer 5 from green light of 555 nm to red light of 650 nm. However, when the light is emitted from the active layer 5 to the GaAs substrate 3, because of the smaller energy band gap of substrate 3, the light is absorbed by the substrate 3 resulting in forming a LED of low efficiency.
To prevent the light absorption of substrate 3, in conventional techniques, a distributed Bragg reflector (DBR) is formed on the GaAs substrate to reflect the light. However, the DBR layer only reflects the incident light nearly perpendicular to the substrate. Therefore, the application of DBR layer is in efficient.
Besides, wafer-bonded transparent substrate (TS) of (AlxGa1xe2x88x92x)0.5In0.5P/GaP LED has been proposed to improve the luminous efficiency. The TS AlGaInP LED is fabricated by the VPE (Vapor Phase Epitaxy) technique to form a p-type GaP window layer with thickness of about 50 xcexcm. And then, the GaAs substrate is removed to expose the n-type AlGaInP lower cladding layer. Furthermore, the exposed n-type AlGaInP lower cladding layer is connected to the n-type GaP substrate.
Because the wafer-bonded technique is directly connecting two types of III-V compound semiconductor together, the process is completed in pressuring and heating at higher temperature. The luminous efficiency of TS AlGaInP LED is twice brighter than that of the absorbing substrate AlGaInP LED. However, because of the complexity of manufacturing layers of TS AlGaInP LED, and high resistance in conductivity between the interface of non-ohmic contact layer, it""s difficult to get high producing yield and lower the cost.
An AlGaInP/metal/SiO2/Si mirror-substrate (MS) LED is proposed in another prior art. The Si substrate and the epitaxial layer are connected by AuBe/Au. However, the luminous intensity of MS AlGaInP LED (about 90 mcd) is 40% less than the luminous density of TS AlGaInP LED in operation current of 20 mA.
The present invention presents a light emitting diode (LED) structure and a method for manufacturing the LED. The LED includes an epitaxial layer formed on an AlGaInP multi-layer epitaxial structure. The AlGaInP multi-layer epitaxial structure is connected to a transparent substrate by a transparent adhesive layer. The material of the AlGaInP multi-layer epitaxial structure is selected from a group consisting of homostructure, single heterostructure (SH), double heterostructure (DH), and multiple quantum well (MQW).
Furthermore, the LED comprises a first ohmic contact layer and a second ohmic contact layer, an electrode connecting channel for electrically coupling a first metal bonding layer to the first ohmic contact layer. Therefore, the first and the second metal bonding layers are in the same side related to the transparent substrate.
The present invention provides a method of manufacturing a light emitting diode. The method includes forming a first ohmic contact layer on an epitaxial structure. Then, the first ohmic contact and the epitaxial structure connect to a transparent substrate via a transparent adhesive layer, such as BCB (B-staged bisbenzocyclobutene), epoxy, and the like. Then, the substrate is removed.
Subsequently, the structure of the LED is etched in two steps. First, a portion of the multi-layer epitaxial structure is removed in width of about 3xcx9c6 mils in etching process to expose the epitaxial layer. Then, the lower portion of the exposed epitaxial layer is removed in width of about 1xcx9c3 mils to form a channel exposing the first ohmic contact layer. A second ohmic contact layer is formed on the lower cladding layer. Then, the first and the second metal bonding layers are connected to the first and the second ohmic contact layers, respectively. Therefore, the first and the second metal bonding layers are in the same side relative to the transparent substrate.
One advantage of the invention is to provide a high-brightness LED readily connected to a transparent substrate at lower temperature to prevent vaporization of group V elements during the adherence process.
Another advantage of the present invention is to provide a high-brightness LED integrated with low cost transparent substrate, such as glass, to improve the production yield at low cost.
Another advantage of the present invention is to provide an electrode channel of better current distribution and smaller voltage when operating at the same current. The electrode channel also improves the emitting efficiency in the same voltage.
Another advantage of the present invention is to provide a high-brightness LED connected to a transparent substrate by soft transparent adhesive layer. Even if the surface of the epitaxial layer is rough, the implement of the transparent adhesive layer is secure.